/Engine/Source/Runtime/Slate/Public/Framework/Docking/TabManager.h
Notify the tab manager that the NewForegroundTab was brought to front and the BackgroundedTab was send to the background as a result.
virtual void OnTabForegrounded ( const [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [SDockTab](API\Runtime\Slate\Widgets\Docking\SDockTab) > & NewForegroundTab, const [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [SDockTab](API\Runtime\Slate\Widgets\Docking\SDockTab) > & BackgroundedTab )